Oily wastes or sludges are undesirable by-products of the separation or recovery of bitumen or heavy oils by surface mining or in situ techniques. Stricter environmental regulations have made the disposal of these wastes more difficult. The recovery operations themselves are energy intensive but in order to meet environmental constraints on sulfur emissions it has been necessary to use clean burning natural gas as the fuel. In the long term the cost of natural gas is expected to rise and ancillary fuels will need to be considered. Combustible wastes such as refinery coke or oily sludge offer a potential alternative to natural gas but their high sulfur content makes them unacceptable as a fuel due to the emission of gaseous sulfur compounds, mainly sulfur dioxide. The reduce such emissions, various methods of desulfurizing fuels have been devised to date in an attempt to capture sulfur at the source of combustion rather than to absorb the gaseous sulfur compounds from the flue gas.
U.S. Pat. No. 4,111,755 to Ban et al. discloses a method of producing a pelletized fixed-sulfur coal or coke. A mixture of coal and a sulfur sorbent (limestone) is ground and blended and then balled or compacted to form pellets. The pellets are then subjected to pyrolysis whereby sulfur is fixed in a calcium compound which remains stable in the ash after the pellets are burned as a fuel.
In a process disclosed in U.S. Pat. No. 4,148,613 to Myers, sulfur-containing solid fuel, e.g. coal, is pulverized and then mixed with a finely divided inorganic material by precipitating the inorganic material such as dolomite or hydroxide or carbonate of sodium, potassium, calcium or barium onto the pulverized fuel. The resulting mixture can be formed into pellets or briquettes by agglomeration using binders or adhesives such as coal tar pitch, petroleum pitch or lignin sulphates. The agglomeration step is provided to improve handling, transportation and storage of the fuel pellets.
In Canadian Patent No. 1,200,778, a process was described in which refinery coke or other carbonaceous waste could be used to separate the hydrocarbons from tailings sludges or other oily wastes such as tank sludges. The result of this process was a solid coke-oil agglomerate and a clean aqueous slurry suitable for disposal. The coke-oil agglomerate has a high sulfur content and hence its use as an ancillary fuel is somewhat limited. If a sulfur capture agent could be incorporated into the agglomerate during the sludge cleaning step then a by-product of the process would be a useable fuel which would not require any additional desulfurization treatment, such as flue gas scrubbing, during combustion.
The problem of desulfurizing potential ancillary fuels from a sludge cleaning process has been addressed in the present research. This work has concentrated on the tar sand bitumen and coke produced in the two oil sand plants operating in Alberta, Canada. The coke produced during the upgrading of Athabasca bitumen contains 6-8 % sulfur almost entirely in the form of organic sulfur compounds. The coke produced in these two plants can be referred to as Suncor delayed coke and Syncrude fluid coke.
It has been found that the coagglomeration of sulfurcontaining carbonaceous material with a sulfur capture agent can be combined with a sludge cleanup operation also resulting in a concomitant beneficiation of the carbonaceous material through the rejection of inorganic impurities. A composite agglomerated fuel may be obtained that offers a relatively high sulfur capture ability on combustion.
Coal is an exemplary carbonaceous material. Where coal washing operations are conducted, waste coal slurry is usually present which is amenable to coagglomeration with oily sludge (waste) from oil refinery storage tanks to give a composite fuel particularly suitable for fluidized bed combustion.